Surface Applied Corrosion Inhibitors For Reinforced Concrete Structures

The process of corrosion is responsible for numerous losses, primarily in reinforced concrete structures. The best way to combat corrosion is prevention. The corrosion inhibitor is one of the recognized and most useful method in the industry to avoid or prevent destruction or degradation of concrete structures; this method is following stand up due to its low-cost and practice method.

Mechanisms Of Actions Of Inhibitors

Inhibitors are substances or mixtures that inhibit, prevent or minimize the corrosion in low concentration and aggressive environment.

The general mechanisms of the inhibitor are highlighted below:

  • The inhibitor is chemically adsorbed (chemisorption) on the surface of the steel. This is followed by the formation of a protective thin film through the inhibitor effect or by a combination between inhibitor ions and surface;
  • The inhibitor leads to formation of a film by oxide protection of the surface.

The corrosion inhibitors function by suppressing the corrosion reaction on the steel reinforcement. The corrosion reaction is an electrochemical reaction with a cathode and anode as illustrated in Fig. 1. The corrosion inhibitors inhibit the reactions at the anode, cathode, or both; those acting at the anode are termed anodic corrosion inhibitors, those at the cathode are cathodic inhibitors and those that suppress the reactions at both are termed ambiotic.

Further, anodic inhibitors are typically the least preferred as they need to be present in a sufficiently high concentration to be effective and are sometimes degenerative (consumed in the inhibition process); thus, sufficient dosage and ongoing dosage may be required. Also, it is reported that some anodic inhibitors may increase the corrosion rate if insufficiently dosed. As ambiotic inhibitors work on both the anodic and cathodic reactions simultaneously, they are usually perceived as being the most efficient.

The inhibition of the anodic reaction rotates the upward sloping line to a steeper gradient (reducing the current produced at each potential) and inhibition of the cathodic reaction similarly rotates the downward sloping line to steeper gradient. Equilibrium is reached where the lines intersect resulting in a lower corrosion current, thereby reducing corrosion activity.

Additionally, unlike surface coatings, corrosion inhibitors have the advantage of providing benefits when the corrosive agents are at the rebar or corrosion has already been initiated.

In the concrete industry, corrosion inhibitors are used in two ways – (a) cast into fresh concrete at the batching plant, and (b) applied topically to existing concrete. The latter method is applicable to repair and maintenance of concrete and is the focus here. Such topically applied corrosion inhibitors are normally referred to as Surface Applied Corrosion inhibitors (SACI).

FAIRMATE offers the perfect solution for reinforced cement concrete structures, that is, FAIRCRETE C-SURFACE APPLIED concrete penetrating corrosion inhibitor.


Fig. 1: Simplified Diagram of the Steel Reinforcement Corrosion Process


FAIRCRETE C-SURFACE APPLIED is a hi-tech corrosion inhibitor system that works on the Bipolar Inhibition Mechanism (B.I.M). B.I.M. inhibits corrosion of steel in concrete at the cathodic pole and anodic pole simultaneously. FAIRCRETE C-SURFACE APPLIED by the virtue of its high vapour pressure and affinity for the embedded metal diffuses through densest concrete to reach the corroding steel.


Fig. 2: Reinforced Corrosion Controls of Bridge
Building Facades  

  Fig. 3: Repair and Protection of


The use of FAIRCRETE C-SURFACE APPLIED for protection of reinforced concrete structures affected by corrosion of steel reinforcement may provide an effective extension of service life. The adoption of FAIRCRETE C-SURFACE APPLIED in the concrete industry almost twenty years ago was done after consideration of several factors, and these factors are still relevant today. These factors are:

  1. How well do penetrating corrosion inhibitors move through concrete, especially when concrete is either carbonated or contaminated with salt-containing chloride ions?

The penetration of FAIRCRETE C-SURFACE APPLIED into reinforced concrete structures affected by carbonation-induced corrosion was found to be satisfactory and was ascribed to the combination of relatively dry concrete, moderate concrete strength and relatively low cover depths to reinforcing steel. Further, though the penetration of surface applied FAIRCRETE C SURFACE APPLIED was slow, it was adequate in structures exposed to carbonation and some airborne salts, typical of structures in coastal locations that are not directly exposed to seawater.

  1. How effectively does FAIRCRETE C-SURFACE APPLIED reduce the rate of corrosion of reinforcing steel that is actively corroding from either carbonation or chloride-induced corrosion?

Corrosion rate monitoring has shown significant medium-term reductions in corrosion rates after treatment with FAIRCRETE C-SURFACE APPLIED. A further reduction in corrosion rates with passivation of corrosion may be achieved when FAIRCRETE C-SURFACE APPLIED is used with coating systems that reduce the internal moisture levels in concrete.

  1. How long will the inhibition of corrosion be effective in reinforced concrete structures that have been treated with penetrating FAIRCRETE C-SURFACE APPLIED?

A majority of the corrosion monitoring which is reported in the literature, was done immediately before application and then for a period of months after treatment with Surface Applied Corrosion inhibitors. It was found that almost all reported structures were either suffering from carbonation-induced corrosion or contained relatively low to moderate levels of chloride ions at the reinforcing. It is generally accepted that corrosion inhibitors can provide up to 15 years of life extension to structures; thus, the long-term performance still needs to be properly assessed.

Moreover, the concrete composition and microstructure must be considered in the evaluation of the performance of corrosion inhibitors, as they may influence several aspects of the concrete in the corrosive process. Therefore, when evaluating inhibitors, it is necessary to verify their composition, mechanism of action and application, along with the aspects related to concrete, and the influence of the inhibitors on the concrete.


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